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The roles water in living organisms and water as a habitat for organisms

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Michael Osgood 2/10/2 The roles water in living organisms and water as a habitat for organisms Introduction Water is the most abundant liquid on the planet. It covers 2/3rds of the earth's surface, and at least 60% of living organisms is water. This value may be as large as 99% - in a jellyfish. The reason for such a large amount of water making up organisms is the fact that it is a major cell constituent - more on that later. Water is a simple molecule yet has many interesting properties which contribute to its importance. Structure Water is made up of two hydrogen atoms bonded to one oxygen atom. They are covalently bonded and the intramolecular covalent bonds are very strong. The structure is non-linear, due to the electron pair repulsion of the two lone pairs of electrons on the oxygen atom. Major cell constituent Often 2/3rds or more of living cells are water. The water is found mainly in the cytoplasm, and it plays a vital role in many functions of the cell: in all organisms - metabolism, and in plants photosynthesis and support. ...read more.


Cerebro-spinal fluid, amniotic fluid, mucus and pleural fluid (the latter in the lungs). All of these are mainly water, and provide either lubrication or protection and cushion, in different ways. Support The turgidity of plants cells is what keeps them upright, and is down to the fact that the cell exerts a force equal to the force of the water entering the cell by osmosis. This balance of force makes the cell stiff. This turgidity helps to support the leaves and stems of many plants. Reactant Reactions are constantly occurring in an organism, catalyzed by enzymes. Water allows many of these reactions to occur, as often the reactants need to be ionized. Water also plays a major part in gaining energy from the sun, as it is a key part in the reaction by which green plants obtain light energy from the sun and store it as chemical energy: 6H2O + 6CO2 C6H12O6 + 6O2 Monosaccharides (such as alpha glucose) join together to by the process of condensation to form larger molecules of starch. ...read more.


This provides an ideal habitat for marine organisms. When mammals get hot, they sweat. Sweat contains mostly water, and therefore a fairly large amount of energy required to evaporate it - this has a large cooling effect on the body. Plants lose water via transpiration, which helps the uptake of nutrient rich water from the soil, and also prevents the temperature of the plant from rising too high. Habitat Water is an ideal medium for life because: * It provides a protective shield * It prevents the cell from drying out * It provides support and buoyancy to organisms * Its good solvency favours the supply of nutrients to the plants, and the removal of waste products from all organisms. * It allows the oxygen required for respiration to be dissolved in it, and its good mobility means it can get virtually anywhere in an organism. * Fertilization - a surrounding body of water disperses the offspring reducing the risk of competition. * Aquatic organisms have very little need for temperature control mechanisms. * Water filters out harmful UV rays from the sun. ...read more.

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